1. Field of the Invention
The invention relates to the provision of a structured medium suitable for the soil-free cultivation of turf and other greenery on the roofs of buildings such as offices or apartment blocks, thereby improving the appearance of said buildings while at the same time providing lawns on which people are free to stroll and relax. Reference is also made to a system for the waterproofing of buildings on which said medium is installed.
2. Description of the Prior Art
The roofs of buildings have for long now been fitted with systems of one sort or another to protect them from water damage. These systems can be divided into two broad types, namely the "protecting concrete" type of system and the "exposed waterproofing" type of system. The use of a protecting concrete type of system involves the laying first of an asphalt waterproofing course and then of the placing a layer of concrete over this in such a way that the asphalt waterproofing course cannot easily be damaged by the application of a concentrated load in any one place. This in turn makes it possible to walk on the roof. The use of the exposed waterproofing type of system, on the other hand, involves the laying of an asphalt waterproofing course only without the addition of a protective concrete covering with the result that the waterproofing course can easily be damaged by the application of a concentrated load. This type of roof covering is not, therefore, suitable for walking on. Bearing in mind the cost of land in urban centers, however, a comparison of these two types of system suggests that better value may be gained from the use of a protecting concrete system which can be walked on on a daily basis. However, the use of a protecting concrete system also necessitates the incorporation of expansion joints into the concrete layer as a means of allowing for thermal expansion and this also, of course, means substantial additional installation time and cost. Repair of the waterproofing layer also necessitates the prior removal of the concrete covering which creates a considerable job management headache of its own.
Moreover, for those living or working on the top floor of a building, the use of either the protecting concrete system or of the exposed waterproofing system gives rise to a similar environmental problem in that when the weather is very hot and the sun causes the roof itself to become extremely hot, the radiant heat heats the roof slab itself and the resultant heat is transferred into the room below. When this occurs there is invariably a most unpleasant sensation of heat radiating from the ceiling even with the air conditioning system running at full power. Artificial turf is also sometimes laid on roofs but this simply serves to improve the appearance of the roof area and has not been found effective in solving the problem of heat. Moreover, even is the roof slab is fitted with some sort of thermal insulation, this cannot completely prevent the conduction of heat into the room below and once the heat has built up inside the room in this way, the thermal insulation materials will then serve only to impede its emission back out of the building during the night.
It is thus currently the case that roofs and other upper areas of buildings are rarely used as anything other than convenient spots for the installation of cooling towers or for the drying of laundry. However, with the proliferation of high rise buildings we have also begun to see more interest being taking in improving the appearance of roof and balcony areas through, example, the laying of turf and the cultivation of flowering plants and shrubs in order to improve the environment by adding to the amount of greenery we are able to enjoy during the course of our daily lives. There are currently two main ways of growing grass and other plants on the roofs of buildings. One of these involves the laying of earth on the roof of a building in order to create a sort of artificial bedding soil. An alternative method involves the use of either rock wool or polyurethane foam for the creation of beds for the cultivation by hydroponic means, for example, of vegetables or flowering plants (for example, Japanese Patent Laying Open No. S55-9739 and S61-25408). However, with the first method outlined above, it is necessary to build up the basic soil bed to a depth of between 10 cm and 20 cm if it is to be possible to walk or sit on and around the turf, plants and shrubs which are eventually grown in this soil. It is also important to take steps to guard against the impairment of the roof waterproofing course through the encroachment of roots into the roof slab and to deal with water leaks. The laying of soil to a depth of 10 cm on the roof will also result in the application of an additional load of approximately 170 kg/m.sup.2 to the roof slab which will consequently require adequate reinforcement. Japanese building standards provide for a maximum permissible live load on roofs or balconies of 180 kg/m.sup.2 and it is clear, therefore, that the regulatory limit could easily be exceeded simply by walking on a roof or balcony covered with this thickness of soil. Soil may also easily be dislodged during rainfall and subsequently come to create a blockage in drainage channels. In the case of the second method outlined above, although there is little chance of the sort of overload problem encountered with the first method, the purpose is hydroponic cultivation which means that it also offers little scope for strolling or even just lying down amidst the greenery.
When considering the addition of greenery to roofs and balconies in the sorts of ways outlined above, it is, of course, also important to find ways of protecting the whole building from damage by water.